Illuminating apparatus and a method of manufacturing an edge light conductor for use therein

ABSTRACT

An illuminating apparatus has a transparent or semitransparent optical medium in the form of an acrylic plate, two fluorescent tubes for emitting light into the acrylic plate through opposite end surfaces thereof, and a reflecting plate disposed under a lower surface of the acrylic plate for upwardly reflecting the light. The lower surface of the acrylic plate defines a diffusing plane including a plurality of irregular reflector regions distributed thereon. The irregular reflector regions comprise ship-shape patterns arranged in juxtaposition longitudinally of the fluorescent tubes. The diffusing plane further includes modified irregular reflector regions formed where the irregular reflector regions are absent. The modified irregular reflector regions irregularly reflect a less quantity of light than the irregular reflector regions.

This is a continuation of copending application Ser. No. 07/973,424filed on Nov. 9, 1992 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an illuminating apparatus and a method ofmanufacturing an edge light conductor for use therein. Moreparticularly, the invention relates to an illuminating apparatuscomprising an edge light conductor including a plate of transparent orsemitransparent optical medium, and light sources opposed to endsurfaces of the plate for introducing light inwardly of the platethrough the end surfaces. The plate has at least one of front and backsurfaces defining a diffusing plane including irregular reflectorregions distributed over the diffusing plane. The invention relates alsoto a method of manufacturing the edge light conductor.

2. Description of the Related Art

This type of illuminating apparatus has a construction as shown in FIG.12. A plate of transparent or semitransparent optical medium receiveslight beams b1, b2, b3 and b4 entering through an end surface 2. Theplate A has a lower surface defining a diffusing plane 8 includingirregular reflector regions 9a and 9b. The beams b1 and b2 areirregularly reflected from the irregular reflector regions 9a and 9b toexit the plate A to illuminate an object.

Light beams, e.g. beams b3 and b4, which do not hit the irregularreflector regions 9 impinge on the upper and lower surfaces of the plateA at incident angles θ not exceeding a critical angle θc, to be totallyreflected. The incident angles are dependent on the angles at which thebeams impinge on the end surface 2 and on the thickness of the plate A.As a result, these beams b3 and b4 continue traveling inside the plateA, instead of exiting the plate A, before reaching the irregularreflector regions 9.

The quantity of exiting light (i.e. illuminating intensity) per unitarea of an illuminating plane of the illuminating apparatus isadjustable by varying areas of the irregular reflector regions per unitarea of the diffusing plane 8.

The irregular reflector region 9b remote from the end surface 2 has alarge irradiated area per unit source area because of a long distancefrom the light source L. In addition, the beam b2 reaches this irregularreflector region 9b after being considerably attenuated as it travelsalong an extended optical path through the plate A. Thus, the beam b2impinges on a unit area of the irregular reflector region 9b in asmaller quantity than the beam b1 impinging on the unit area of theirregular reflector region 9a close to the end surface 2. Naturally,therefore, the irregular reflector region 9b provides a reduced quantityof irregular reflection per unit area.

In order for the illuminating apparatus to have a uniform illuminatingintensity throughout the illuminating plane, the quantity of irregularreflection must be uniformed throughout unit areas of the diffusingplane 8.

A plate A in a conventional illuminating apparatus of this defines adiffusing plane 8 including irregular reflector regions 9 as shown inFIG. 13. The irregular reflector regions 9 are distributed such that theareas thereof occupying unit areas of the diffusing plane 8 are largerin positions 8b remote from end surfaces 2 of the plate A than inpositions 8a close thereto.

According to the prior art noted above, it is necessary to secure largeregions 13 of the diffusing plane 8 in the positions 8a close to the endsurfaces 2 where no irregular reflector regions 9 are formed, in orderthat the irregular reflector regions 9 are larger in the positions 8bremote from the end surfaces 2 than the positions 8a close thereto.These regions 13 are left to be smooth and transparent regions producinglittle or no effect of irregular reflection.

Thus, the diffusing plane 8 produces the less total quantity ofirregular reflection for the regions 13 where no irregular reflectorregions 9 are formed. This results in the inconvenience that theilluminating apparatus becomes dark with the illuminating intensityreduced for uniformity. The conventional construction also has adisadvantage of failing to use the light from the light sourceseffectively.

In the prior art, the quantity of irregular reflection per unit area isadjusted by means of the irregular reflector regions and transparentregions. This inevitably results in lack of uniformity in illuminatingintensity over the illuminating plane of the apparatus since theirregular reflector regions and transparent regions produce a greatdifference in illuminating intensity (contrast). Specifically, thepatterns of the irregular reflector regions 9 distributed as shown inFIG. 13 appear on the illuminating plane of the apparatus.

SUMMARY OF THE INVENTION

The object of the present invention is to eliminate the disadvantages ofthe prior art noted above.

This object is fulfilled, according to the present invention, by anilluminating apparatus as noted in the outset hereof, in which thediffusing plane further includes modified irregular reflector regionsformed in at least some of the parts thereof from which the irregularreflector regions are absent, the modified irregular reflector regionsproviding a less quantity of irregular reflection than the irregularreflector regions.

With the above construction in which modified irregular reflectorregions are formed in the pans of the diffusing plane having noirregular reflector regions, the quantity of irregular reflection perunit area of the diffusing plane may be adjusted by varying a ratiobetween the irregular reflector regions and modified irregular reflectorregions occupying the unit areas of the diffusing plane. At the sametime, the light emitted from light sources is irregularly reflected bythe modified irregular reflector regions also.

Since the modified irregular reflector regions also reflect the lighttraveling from the light sources, the illuminating intensity on theilluminating plane of the apparatus may be increased while the intensityper unit area of the illuminating plane is adjustable. The quantity ofirregular reflection per unit area is adjusted by means of the irregularreflector regions and modified irregular reflector regions. Theirregular reflector regions and modified irregular reflector regionshave a smaller difference in illuminating intensity (contrast) than theirregular reflector regions and transparent regions. Thus, the quantityof irregular reflection may be adjusted with subtle variations inilluminating intensity. Consequently, the irregular reflector regionsdistributed over the diffusing plane are invisible on the illuminatingplane of the apparatus.

Thus, the illuminating apparatus according to the present inventionprovides increased brightness and minimal unevenness in illuminatingintensity on the illuminating plane though the same light sources as inthe prior an are used.

In the illuminating apparatus according to the present invention, theirregular reflector regions may be formed on the diffusing plane suchthat a greater quantity of light is irregularly reflected from positionsremote from the end surfaces than from positions close thereto.

With this arrangement, illuminating intensity may be uniformedthroughout the diffusing plane. This apparatus provides increasedbrightness while uniforming illuminating intensity throughout thediffusing plane.

The irregular reflector regions and modified irregular reflector regionsmay comprise rugged surfaces formed on the plate.

With this construction, the irregular reflector regions and modifiedirregular reflector regions produce a greater effect of irregularreflection than in the prior art. In the prior art, the irregularreflector regions are formed by applying a hypochromatic white ink ormilky paint mixed with glass beads or other diffusing materials, to aplate surface by a printing technique.

In the prior art, the irregular reflector regions are formed by applyingink or paint to a smooth plate surface. Since an interface between plateand ink or paint reflects a certain quantity of light, part of the lightimpinging on the irregular reflector regions is reflected by theinterface to return inwardly of the plate without reaching the ink orpaint. Consequently, a reduced quantity of light is irregularlyreflected by the irregular reflector regions. The part of light reachingthe ink or paint is attenuated through repeated irregular reflectionswithin the layer of ink or paint. Further, the irregularly reflectedlight exiting the ink or paint may be blocked by pigments or diffuserparticles present on optical paths. The effect of irregular reflectionis impaired in this way. However, such an inconvenience is eliminatedwhere the irregular reflector regions and modified irregular reflectorregions are in the form of rugged surfaces, thereby to enhance theeffect of irregular reflection.

Consequently, the illuminating apparatus according to the presentinvention provides increased brightness with the enhanced effect ofirregular reflection produced by the irregular reflector regions andmodified irregular reflector regions.

In a further aspect of the invention, a method of manufacturing an edgelight conductor is provided which comprises the steps of shaping atleast one of front and back surfaces of a plate of transparent orsemitransparent optical medium to be a uniform rugged surfacesubstantially throughout an entirety thereof, and forming modifiedirregular reflector regions by applying deposits to part of the ruggedsurface to limit a quantity of irregular reflection.

With this method, there is no need to form graphic patterns of theirregular reflector regions with great subtlety and ultra-high precisionin the process of forming the rugged surface. The parts having thedeposits act as the modified irregular reflector regions.

Thus, the present invention provides a method of easily and quicklymanufacturing an edge light conductor having a high efficiency ofirregular reflection and assuring bright edge light.

The parts having the deposits to act as the modified irregular reflectorregions may retain a certain quantity of irregular reflection caused bythe rugged surface lying underneath the deposits. With this arrangement,the modified irregular reflector regions may cause irregular reflectionwhile the illuminating intensity of the edge light is adjustable by adistribution ratio between the irregular reflector regions and modifiedirregular reflector regions. Thus, the edge light conductor manufacturedby this method provides an increased total quantity of irregularreflection to assure brightness.

The rugged surface may advantageously be formed by sand blasting.

In this way, the rugged surface may be formed substantially uniformly,simply and quickly over the entire or approximately entire surface ofthe plate for defining the irregular reflector regions.

The modified irregular reflector regions may be formed by applyingtransparent ink in a printing process to form the deposits.

With this method, the transparent ink applied to the rugged surfaceproduces the same effect as water adhering to ground glass, to limit thequantity of irregular reflection from the rugged surface. Sincetransparent ink is applied by printing, very fine and accurate graphicpatterns of the irregular reflector regions may be formed simply andquickly. Thus, this method is capable of simply and quicklymanufacturing an edge light conductor that provides a preciselyregulated illuminating intensity.

The transparent ink may be applied by a printing technique such asphotographic printing using a photoresist or by silk screen printing,for example. Then, the transparent ink applied has an unsmooth surfaceas distinct from a smooth surface formed by a mirror die or mirrorroller. In the case of silk screen printing, the surfaces of thetransparent ink deposits have fine traces left by silk screen meshes,thereby defining rugged surfaces for causing a certain quantity ofirregular reflection.

Thus, the modified irregular reflector regions may be formed simply byapplying the transparent ink in a printing process.

Other features and advantages of the invention will be apparent from thefollowing more particular description of preferred embodiments of theinvention, as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view in vertical section of an ultra-thin light boxaccording to the present invention,

FIG. 2 is a perspective view showing a diffusing plane of a platemounted in the light box,

FIGS. 3 (A) and (B) are sectional views showing a method of forming thediffusing plane,

FIG. 4 is a perspective view showing a diffusing plane in anotherembodiment,

FIG. 5 is a perspective view showing a diffusing plane in a furtherembodiment,

FIG. 6 a fragmentary sectional view of an illuminating apparatus in astill further embodiment,

FIG. 7 a fragmentary sectional view of an illuminating apparatus in astill further embodiment,

FIG. 8 a fragmentary sectional view of an illuminating apparatus in astill further embodiment,

FIG. 9 is an enlarged view showing a deposit on a plate in a stillfurther embodiment,

FIG. 10 is an enlarged view showing a deposit on a plate in a stillfurther embodiment,

FIG. 11 is an enlarged view showing a deposit on a plate in a stillfurther embodiment,

FIG. 12 is a schematic view showing functions of a diffusing plane of aplate, and

FIG. 13 is a perspective view showing a diffusing plane of aconventional apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Illuminating apparatus according to the present invention will bedescribed in detail with reference to the drawings.

FIG. 1 shows an edge light type ultra-thin light box in one embodimentof the present invention.

This ultra-thin light box comprises a casing P having an upper surfacedefining an illuminating plane. A positive photograph or film such as aslide photograph may be placed on the illuminating plane for observationby means of transmitted light.

A milky, semitransparent acrylic plate 1 is mounted on the illuminatingplane of the casing P to act as an edge light conductor. Light emittedfrom the illuminating plane has a color temperature adjustable to 5,000degrees, for example.

The casing P contains a transparent or semitransparent optical medium inthe form of an acrylic plate A, two fluorescent tubes L acting as lightsources for emitting light into the acrylic plate A through opposite endsurfaces 2 thereof, and a circuit device 3 for lighting the fluorescenttubes L.

The fluorescent tubes L may be the cold cathode type or hot cathodetype.

A battery 5 is connected to an outer position of the casing P through apin jack 4 to supply power to the fluorescent tubes L.

Power may be derived also from a household AC outlet by using an ACadapter connected through the pin jack 4.

Each of the fluorescent tubes L has a reflector 6 attached thereto,whereby light emitted from each fluorescent tube L is all directed tothe end surface 2 of the acrylic plate A. A reflecting plate 7 isdisposed opposite a lower surface of the acrylic plate A. The reflectingplate 7 has an upper surface defining a mirror surface, whereby lightemerging from the lower surface of the acrylic plate A is reflectedtoward the upper surface thereof. The acrylic plate A is disposeddirectly under the illuminating plane, and the lower surface of theacrylic plate A defines a diffusing plane 8.

FIG. 2 shows the fluorescent tubes L and acrylic plate A, with thediffusing plane 8 revealed. The diffusing plane 8 includes a pluralityof irregular reflector regions 9 distributed thereon.

The irregular reflector regions 9 comprise ship-shape patterns arrangedin juxtaposition. The ship-shape patterns are elongated toward thefluorescent tubes L, and arranged side by side in the longitudinaldirection of the fluorescent tubes L substantially throughout thediffusing plane 8.

Thus, the irregular reflector regions 9 are formed such that a greaterquantity of light is irregularly reflected in positions 8b remote fromthe end surfaces 2 than in positions 8a close thereto.

For clarity of illustration, FIG. 2 shows the ship-shape patternsforming the irregular reflector regions 9 as considerably enlarged inrelation to the entire illuminating apparatus. In fact, these patternsare formed very narrow, very large in number, and finished withultra-high precision. The diffusing plane 8 further includes modifiedirregular reflector regions 10 formed where the irregular reflectorregions 9 are absent. The modified irregular reflector regions 10irregularly reflect a less quantity of light than the irregularreflector regions 9.

In this embodiment, the modified irregular reflector regions 10 fill theentire area of the diffusing plane 8 in which the irregular reflectorregions 9 are not formed. The irregular reflector regions 9 and modifiedirregular reflector regions 10 comprise rugged surfaces formed on theacrylic plate A.

It is also possible to form the irregular reflector regions 9 andmodified irregular reflector regions 10 by applying a hypochromaticwhite ink or milky paint mixed with glass beads or other diffusingmaterials, to a surface of a plate by a printing technique as describedlater.

The above-noted rugged surfaces may be formed by various methods such asinjection molding, die casting such as solven casting, cutting, etching,electric discharge machining, photographic printing using a photoresistor an ultraviolet hardenable substance, and sand blasting describedhereinafter.

In this embodiment, the rugged surfaces are formed as follows.

An acrylic plate having smooth surfaces providing almost no irregularreflection (such a plate is readily available in commerce) is cut tosize, and the end surfaces 2 are formed to define smooth planes forreceiving light from the light sources.

One of the upper and lower surfaces of the acrylic plate A is used todefine the diffusing plane 8. First, as shown in FIG. 3 (A), a ruggedsurface is formed over the entire diffusing plane 8 by sand blasting.This rugged surface has a degree of roughness adjustable by selectingsize, blasting intensity, blasting time and the like of an abrasive usedin the sand blasting.

In fact, what is known as a diffuser plate or diffuser sheet having sucha rugged surface already formed is commercially available also. Such aproduct may be used instead.

Next, as shown in FIG. 3 (B), an acrylic transparent ink is applied bysilk screen printing technique to portions of the rugged surface forforming the modified irregular reflector regions 10. This ink formsdeposits to limit irregular reflection. The ship-shape patterns shown inFIG. 2 are left free of the ink deposits.

The transparent ink may be applied to the modified irregular reflectorregions 10 by other printing techniques than silk screening. Forexample, a photoresist polymer may be applied in buildup form.

The transparent ink produces the same effect as water adhering to groundglass, to reduce irregular reflection from the rugged surface.

In this embodiment, as noted above, the transparent ink is applied tothe modified irregular reflector regions 10 by silk screen printing. Thesurfaces of the transparent ink deposits have traces left by silk screenmeshes, thereby defining rugged surfaces with a certain degree ofroughness. In addition, the original, rugged surface lies underneath theink deposits. The portions of the lower surface 8 of the acrylic plate Ato which the transparent ink has been applied, therefore, causeirregular reflection in an appropriate degree, instead of eliminatingthe irregular reflection altogether. Thus, these portions provide themodified irregular reflector regions 10.

The portions of the rugged surface remaining in the ship-shape patterns,as they are, act as the irregular reflector regions 9.

The quantity of irregular reflection from the modified irregularreflector regions 10 is adjustable by varying the degree of roughness ofthe transparent ink surfaces or by mixing an irregularly reflectingadditive into the transparent ink.

The illuminating apparatus in this embodiment, as constructed above, hasshown an improvement in illuminating intensity of about 40-50% over aconventional illuminating apparatus without the modified irregularreflector regions 10. In the conventional illuminating apparatus, theirregular reflector regions distributed over the illuminating plane areclearly discernible in the naked eye. By contrast, the illuminatingapparatus in this embodiment provides a substantially uniform intensityof illumination, with no visible variation, throughout the illuminatingplane.

The irregular reflector regions 9 are not limited to the ship-shapepatterns, but may be in the form of triangles, groups of lines, or dots.

Other embodiments will be described next.

FIGS. 4 and 5 show reflector regions formed of dot patterns. Thediffusing plane 8 shown in FIG. 4 includes irregular reflector regions 9formed of a plurality of dots having different sizes. These dots are thesmaller toward the end surfaces 2 and the larger away therefrom.

The diffusing plane 8 shown in FIG. 5 includes a plurality of dotshaving different sizes and formed in portions other than the irregularreflector regions 9. These dots provide the modified irregular reflectorregions 10, which are the larger toward the end surfaces 2 and thesmaller away therefrom.

Thus, the irregular reflector regions 9 in FIGS. 4 and 5 are arrangedsuch that light is irregularly reflected in a greater quantity inpositions 8b of the diffusing plane 8 remote from the end surfaces 2than in positions 8a thereof close to the end surfaces 2.

The irregular reflector regions 9 are not limited to the function touniform the illuminating intensity on the illuminating plane of thelight box, but may be adapted to vary the intensity for certain parts ofthe illuminating plane.

The modified irregular reflector regions 10 may be formed in onlycertain of the parts of the diffusing plane 8 where the irregularreflector regions 9 are not formed.

The quantity of irregular reflection from the modified irregularreflector regions 10 need not be uniform through the diffusing plane 8.Plural types of modified irregular reflector regions 10 providing variedquantities of irregular reflection may be distributed over the diffusingplane 8.

The diffusing plane 8 may be formed on each of the upper and lowersurfaces of the acrylic plate A.

The light box may include a plurality of acrylic plates A as shown inFIGS. 6, 7 and 8.

As shown in FIG. 7, the light box may further include an irregularreflector plate 11 disposed under the acrylic plates A and defining anirregularly reflecting ragged surface 11a.

As shown in FIG. 8, the bottom acrylic plate A may have an upper surfacedefining the diffusing plane 8 and a lower surface defining anirregularly reflecting rugged surface 12.

The illuminating apparatus is not limited to the ultra-thin light box,but may comprise a backlight apparatus for a display device or for aliquid crystal display of an office automation product, for example.

FIGS. 9, 10 and 11 show, in enlargement, the modified irregularreflector regions 10 having transparent ink deposits. As shown in FIG.9, the modified irregular reflector regions 10 may include bubbles 14formed in recesses of the rugged surface as a result of incompletefilling with the transparent ink.

As shown in FIG. 10, the modified irregular reflector regions 10 mayhave rugged surfaces 10a formed by deposits to produce irregularreflection.

As shown in FIG. 11, the modified irregular reflector regions 10 may beformed of a thin layer of transparent ink through which ridges of therugged surface project to a certain extent.

The deposits defining the modified irregular reflector regions 10 may beformed of any other material than the acrylic transparent ink, as longas it is effective to reduce irregular reflection. For example, amaterial in sheet form may be used, or a chemical may be used todissolve the ridges of the rugged surface for smoothness.

The method of forming the modified irregular reflector regions 10 is notlimited to the uniform application of transparent ink to the lowersurface 8. The type of ink, the method or mode of application may bevaried as appropriate, to form plural types of modified irregularreflector regions having different quantities of irregular reflectionand distributed over the lower surface 8.

As noted in the first embodiment, the irregular reflector regions 9 arenot limited to the ship-shape patterns, but may be in the form oftriangles, groups of lines, or dots.

The plate of transparent or semitransparent optical medium is notlimited to the acrylic plate A. Glass or various plastics (e.g.polyethylene, polyester and epoxy resin) may be employed instead.

What is claimed is:
 1. An illuminating apparatus comprising:an edgelight conductor including plate means of transparent or semitransparentoptical medium having end surfaces and at least one of front and backsurfaces defining a diffusing plane, said diffusing plane includingirregular reflector regions distributed over a portion of said diffusingplane, said diffusing plane further including modified irregularreflector regions formed in a remainder of said diffusing plane, withsaid modified irregular reflector regions providing a lesser quantity ofirregular reflection than said irregular reflector regions, with saidirregular reflector regions formed on said diffusing plane such that agreater quantity of light is irregularly reflected from positions remotefrom said end surfaces than from positions close thereto and with saidirregular reflector regions and said modified irregular reflectorregions including rugged surfaces formed on said plate means; and lightsources opposed to said end surfaces of said plate means for introducinglight inwardly of said plate means through said end surfaces.
 2. Anilluminating apparatus as defined in claim 1, wherein said plate meansincludes an acrylic plate.
 3. An illuminating apparatus as defined inclaim 1, wherein said irregular reflector regions comprise a pluralityof ship-shape patterns elongated toward said light sources and arrangedside by side in a longitudinal direction of said light sourcessubstantially throughout said diffusing plane.
 4. An illuminatingapparatus as defined in claim 3, wherein said plate means includes aplurality of acrylic plates.
 5. An illuminating apparatus as defined inclaim 4, wherein a lowermost one of said acrylic plates has an uppersurface defining said diffusing plane and a lower surface defining anirregularly reflecting rugged surface.
 6. An illuminating apparatus asdefined in claim 1, wherein said irregular reflector regions comprisedot patterns formed of a plurality of dots having different sizes, saiddots being the smaller toward said end surfaces and the larger awaytherefrom.
 7. An illuminating apparatus as defined in claim 6, whereinsaid plate means includes a plurality of acrylic plates.
 8. Anilluminating apparatus as defined in claim 1, wherein said modifiedirregular reflector regions comprise dot patterns formed of a pluralityof dots having different sizes, said dots being the larger toward saidend surfaces and the smaller away therefrom.
 9. An illuminatingapparatus as defined in claim 1, wherein said plate means includes aplurality of acrylic plates.
 10. An illuminating apparatus as defined inclaim 9, further comprising an irregular reflector plate disposed undersaid acrylic plates and defining an irregularly reflecting ruggedsurface.
 11. An illuminating apparatus as defined in claim 9, wherein alowermost one of said acrylic plates has an upper surface defining saiddiffusing plane, and a lower surface defining an irregularly reflectingrugged surface.
 12. The illuminating apparatus as defined in claim 1,wherein said modified regular reflector region includes a depositattached to said rugged surface.
 13. The illuminating apparatus asdefined in claim 12, wherein said deposit includes transparent inkapplied to said rugged surface.
 14. The illuminating apparatus asdefined in claim 13, wherein each said deposit has a non-smooth uppersurface.
 15. An illuminating apparatus comprising:an edge lightconductor including plate means of transparent or semitransparentoptical medium having end surfaces and at least one of front and backsurfaces defining a diffusing plane, said diffusing plane includingirregular reflector regions distributed over a portion of said diffusingplane, said diffusing plane further including modified irregularreflector regions formed in a remainder of said diffusing plane, withsaid modified irregular reflector regions providing a lesser quantity ofirregular reflection than said irregular reflector regions; and lightsources opposed to said end surfaces of said plate means for introducinglight inwardly of said plate means through said end surfaces.
 16. Anilluminating apparatus as defined in claim 15, wherein said modifiedirregular reflector regions include rugged surfaces formed on said platemeans with deposits attached to said rugged surfaces.
 17. Theilluminating apparatus as defined in claim 16, wherein said depositsinclude transparent ink applied to said rugged surfaces.
 18. Theilluminating apparatus as defined in claim 16, wherein each said deposithas a non-smooth upper surface.
 19. An illuminating apparatuscomprising:an edge light conductor including plate means of transparentor semi-transparent optical medium having end surfaces, at least oneother surface defining a defusing plane, irregular reflector regionsdistributed over a portion of said diffusing plane, wherein saidirregular reflector regions include rugged surfaces formed on said platemeans, modified irregular reflector regions formed on said plate meansin parts thereof from which said irregular reflector regions are absent,wherein said modified irregular reflector regions include ruggedsurfaces formed on said plate means with deposits attached to saidrugged surfaces, and wherein said modified irregular reflector regionsprovide a lesser quantity of irregular reflection than said irregularreflector regions; and light sources opposed to said end surfaces ofsaid plate means for introducing light inwardly of said plate meansthrough said end surfaces.